Exploring Forward Osmosis: Is It Worth It?

By Taylor Schaefer, Writing Project Leader for Save The Water™ | June 5, 2015

Increased agricultural production and global population has put pressure on our already limited water sources. As freshwater becomes a scarcer commodity around the world, companies are seeking new ways to reuse and replenish sources in a more efficient and environmentally friendly way. Methods such as desalination and reverse osmosis have played a significant role in creating new water sources. However, high-energy consumption poses a problem for a changing climate. (2) Forward osmosis is a process that is currently being explored and tested more frequently. Experts seek to discover the effectiveness of the process to produce freshwater from the dirtiest wastewaters in which reverse osmosis cannot. (1)

Currently 21 billion gallons of fresh water is desalinated worldwide each day.  The majority of that water is a result of reverse osmosis. (1) Reverse osmosis pumps pressurized water through a series of membranes to remove the salt, but this method still requires a significant amount of energy. Instead of forcing the water through the membrane, forward osmosis is pushed through naturally from a concentrated to less concentration solution, requiring less energy. Using forward osmosis a company called Oasys Water was able to turn roughly 60 percent of oil and gas wastewater into safe drinking water. This water is too saline to treat with reverse osmosis and would burst the membrane. (1)

While the nature motion of forward osmosis require less energy, a study from Massachusetts Institute of Technology claims that forward osmosis is less energy efficient than reverse osmosis because it involves two steps. First, the water is drawn into a concentrated solution called draw solution, and then a second step is required to produce purified water from the draw solution. The study states since the salt content in the draw solution is of such a higher concentration than seawater, it will always require a higher level of energy for regeneration. (3)

Since these processes are still being researched, there is an ongoing to debate on whether forward osmosis will prove to be a viable solution to the world’s water problems. So far it has proven it can clean much dirtier water than reverse osmosis can, but the question of whether it is worth the energy consumption still remains. Can the process be altered to become more energy efficient? Companies are working on different forms of forward osmosis to prove just that. Researchers are exploring numerous techniques including filtering through magnetic fields, or skimming oil based salts off the top of the draw solution in order to reduce energy consumption in the regeneration process. (1)

Using fertilizer drawn forward osmosis for agriculture is also being explored. Instead of using extra energy to regenerate the draw solution, a fertilizer is used in the first step. A diluted fertilizer solution is created after desalination that can be directly applied to crops, removing the second process of regeneration. Since the agricultural sector constitutes up 70 percent of the world’s freshwater withdrawal this could be a major asset to water conservation efforts. (2)

As the world’s access to fresh water sources continues to diminish, it is imperative that researchers continue to find more sustainable and efficient alternatives in order to provide for a consistently growing population.  Experimenting with processes like forward osmosis brings the world closer to developing improved methods of conservation and distribution of freshwater.

Sources:

1. McKenna,Phil. 29 April 2015. ”Purifying the Dirtiest Waters.” PBS. https://www.pbs.org/wgbh/nova/article/forward-osmosis/
2. Phuntsho, S., Shon, H., Hong, S., Lee, S., Vigneswaran, S., & Kandasamy, J. “Fertiliser drawn forward osmosis desalination: the concept, performance and limitations for fertigation.” Reviews In Environmental Science And Bio-Technology, 11(2), 147-168.
3. Water World. 25 July 2014.“Forward osmosis is not energy efficient, says MIT study.” Waterworld.com. https://www.waterworld.com/municipal/drinking-water/treatment/article/16215387/forward-osmosis-is-not-energy-efficient-says-mit-study